The present invention relates to a voice encoding/decoding apparatus coping with a modem signal and, more particularly, to a voice encoding/decoding apparatus which encodes an input signal as a voice signal using a voice encoding means, decodes the signal using a voice decoding means, and outputs it, or directly transmits an input signal as a non-voice signal through the voice encoding and decoding means.
In a conventional voice encoding/decoding apparatus aiming at transmission of not only voice signals but also non-voice signals, when an input non-voice signal is detected on the encoding side, the non-voice signal is temporarily decoded using a demodulator corresponding to the modulation scheme. -The decoded data is transmitted in place of encoded voice data. On the decoding side, the transmitted decoded data is not decoded using a voice decoder but modulated using a modulator corresponding to the modulated signal input to the encoding input side, thereby transmitting the non-voice signal.
As such a conventional voice encoding/decoding apparatus, a technique of controlling switching between a non-voice signal and a voice signal using an identification signal while cascade-connecting demodulators has been proposed.
Japanese Patent Laid-Open No. 5-122414 discloses a voice encoding/decoding apparatus for ON/OFF-controlling modulators/demodulators by detecting a G3 facsimile signal as a non-voice signal. Japanese Patent Laid-Open No. 2-246535 discloses a voice information transmission method of transmitting a PB (Push Button) signal by a unique scheme using a determination bit.
In the prior arts, however, since a non-voice signal is temporarily decoded to transmit data, the voice encoding unit must have modulators/demodulators equal in number to non-voice signal modulation/demodulation schemes.
In addition, since data obtained by demodulating a non-voice signal is transmitted in place of a voice signal to a line with the same transfer rate as that for a voice signal, the data transfer rate is limited to a rate lower than that transfer rate of the voice encoding/decoding apparatus.
Japanese Patent Laid-Open No. 63-26044 discloses a voice encoding apparatus for compressing voice information and transmitting a modem signal like a voice signal.
Japanese Patent Laid-Open No. 63-141423 discloses a voice encoding/decoding apparatus having, on the transmission side, two encoders for encoding a voice signal and a modem signal, respectively, and a means for transmitting a signal representing the type of signal to be transmitted to the reception side, and on the reception side, two decoders for decoding an encoded voice signal and an encoded modem signal, respectively. This encoding/decoding apparatus selects a decoder in accordance with the type of encoded signal from the transmission side.
Japanese Patent Laid-Open No. 7-143076 discloses an encoding/decoding apparatus which uses, on the encoding side, a voice signal code book when an input signal is a voice signal, and a modem signal code book when an input signal is a modem signal, and on the decoding side, determines the received signal added with information identification and decodes the data using the voice signal code book when the input encoded data is voice signal encoded data, and using the modem signal code book when the input encoded data is modem signal encoded data.
However, in the above-described prior art as well, no solutions to the requirement of modulators/demodulators equal in number to corresponding modulation/demodulation schemes are disclosed. Additionally, any means of increasing the data transfer rate according to the improvement of voice encoding/decoding scheme are not disclosed, either.
Modulation/demodulation schemes of many types are put into practice and widely used, and the conventional apparatuses must have all modulators/demodulators corresponding to these schemes.
When specification expansion unique to a modulator/demodulator is done by the unit developer, it is impossible to cope with a signal which can be determined as a non-voice signal as far as the use expansion is unique to the developer or maker of the unit.
In a line connected for data transmission, which not assumed by the modulator/demodulator, processing of temporarily demodulating and then modulating data is performed midway. This processing causes a delay to degrade the line quality.
To demodulate and transmit a non-voice signal, the same line as that used to encode and transmit a voice signal is used. For this reason, the non-voice signal transfer rate must be lower than the voice signal transfer rate. In association with this point, along with the recent progress in research and development, voice encoding schemes using lower bit rates are being developed.
On the other hand, modulation/demodulation schemes are being developed to increase transfer rates. In the prior arts, however, a modulated/demodulated signal must also be transmitted using a line for a voice encoding/decoding scheme using a low bit rate. For this reason, the line quality for the modulator/demodulator is apparently low, and transmission is performed at a transfer rate lower than that of the line for the voice encoding/decoding scheme.
In addition. in a high-efficiency voice encoding scheme, an encoded voice signal may degrade due to not only the characteristics of an input voice signal and the S/N ratio but also background noise contained in the input voice signal.